1. Field of the Invention
This invention relates to a push-type switch used in electronic equipment, and specifically relates to a switch turning on and off as a result of ends of a built-in coil spring connecting and disconnecting with contact terminals.
2. Description of Related Art
For example, a “switch” as disclosed in Japanese Laid-open Patent Publication No. Hei. 7-93074 (related art 1) is provided where a conductive spring is built-into a casing, so that the switch is made to go on and off as a result of contact pieces freely making and breaking contact with connection terminals provided on the inside surface of the box. The “switch” of related art 1 is comprised of a substantially box-shaped case where fixing elements are implanted in a planar manner in an inner bottom surface, a coiled spring contacting piece having a moving end having a springy conductive member curved in the shape of a U with a contact point at an end thereof curved substantially in a semi-circle shape and a fixing end having a contact point at an end thereof while being substantially straight, an operating body constituted by a substantially cylindrical molded member having an inverted c-shaped groove at one end, sliding in a longitudinal direction so as the inverted c-shaped groove traverses the moving end of the contact piece, and a cover supporting the operating body coupled to the case in a slidable manner and sandwiching the coil of the contact piece together with the case.
In related art 1, as shown in FIG. 15, fixing terminals 112 and 113 are provided at the bottom surface within the case 111. A contact piece 114 made of a conductive member having springiness is provided within the case 111. The contact piece 114 is provided such that one end of a coiled spring section 114e is curved in a U-shape, and is formed with a moveable end 114b having a contact point 114c bent in a substantially semi-circular shape at one end, and the other end is in a rectilinear shape forming a fixing end 114a having a contact point 114d making contact with the fixing terminal at the front end.
A contact piece 114 forming a fixing end 114a having a contact point 114d making contact with the terminal 112 is provided.
An operating body 115 is substantially cylindrical and has an inverted c-shaped groove 115a at one end. This groove 115a spans the movable end 114c of the contact piece 114 and is made to slide in a longitudinal direction so that the contact point 114c and the fixing terminal 113 connect and disconnect.
The cover 116 is a lid containing the contact piece 114 within the upper part of the case 111. The cover 116 has a hole 116a supporting the operating body 115 in a manner capable of sliding, links with the case 111, and has a projection 116b sandwiching the coil section 114e of the contact piece 114 together with a u-shaped depression 111a of the case 111.
In the related art 1 formed in this manner, the moveable end 114b is caused to move downwards as a result of the operating body 115 being pressed downwards so as to slide in a manner resisting spring force of the contact piece 114. At this time, the moveable end 114b is made to move according to the spring force of a coil spring and a curve of the moveable end 114b as a result of a spring section 114e moving in a winding direction of the coiled spring taking the contact point 114d making contact with the contact terminal 112. The contact point 114c moves in a horizontal direction in FIG. 15 as a result of the moveable end 114b moving in a downward direction, and is moved to the position of the fixing terminal 113 so as to make contact with the fixing terminal 113, so that the fixing terminal 112 and the fixing terminal 113 enter a conducting state.
Further, when the thrust of the operating body 115 ends, the contact piece 114 returns to its original position due to its own spring force, the contact point 114c is separated from the fixing terminal 113, and the fixing terminal 112 and the fixing terminal 113 enter an insulating state.
However, with the switch of related art 1, the operating body 115 is slid downwards so that the fixing end 114a and the moveable end 114b of the contact piece 114 make contact with the fixing terminal 112 and fixing terminal 113. However, the operating force acting against movement in a downward direction and the contact force necessary in contact between the contact terminal 113 and the fixed terminal 114a and contact between the contact terminal 113 and the moveable end 114b is made by the resilient force due to torsion in the winding direction of the spring section 114e of the contact piece 114.
Resilient force generated by torsion in the winding direction of the coil spring changes according to the amount of torsion. It is therefore difficult to maintain a set value for contact pressure between the contact piece and the fixing terminal.
In particular, with push switches for detecting position used in various electronic equipment for detecting a position of a CD tray etc. of a CD player or computer etc., the operation force used in pressing the push switch is 0 and contact pressure between the contact piece and the fixing terminal is ideally a set value. In the related art example, when the operation force pressing the push switch is made small, contact pressure between the contact piece and the fixing terminals becomes small and there is therefore the problem that the operation force has to be large to implement the set contact pressure. When operation force is made small, the contact pressure is also made small, and contact pressure at a contact start position for the contact piece and the fixing terminal and contact pressure at a time when the contact piece further moves after contact become different. Contact resistance at the contact start position therefore becomes large, errors occur at positions judged to be conducting, and detected position precision therefore becomes poor.
The operation direction of the contact piece due to the operating body deforms the contact piece in the winding direction of the coil spring. This therefore made it difficult to make the operation direction of the switch short.
In order to resolve the aforementioned problems, this invention is advantageous in providing a switch where change in contact pressure due to the position of a contact piece is small.